This application is a continuation of U.S. patent application Ser. No. 09/710,362, filed Nov. 10, 2000, now U.S. Pat. No. 6,757,313, which claims the benefit of U.S. Provisional Application No. 60/164,864, filed Nov. 12, 1999. The entire contents of the prior applications are incorporated herein in their entirety by reference. The present application relates to controlling the lateral extent of a region of a semiconductor laser diode that is exposed to a gain current, and specifically to controlling such lateral extent in a ridge waveguide semiconductor laser diode adapted to support selected lateral modes of the emitted laser light.